This investigation is concerned with the problem of how and by what pathways visceral afferents can modify cortical PT-neuron activity. Extracellular and intracellular recordings of single PT-neurons will be obtained in the motor cortex of adult cats. The response patterns of these neurons will be studied during periods when visceral afferents are stimulated using techniques such as electrical stimulation of the vagus nerve, inflation of a balloon in the carotid sinus, intravenous and intra-arterial injections of drugs such as phenyldiguanide, etc. The effects on PT-cells of visceral afferents from different sites and with different functions will also be studied by stimulation at selected sites, e.g. lung inflation.